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Selection of working fluid is one of the main criterions for designing of heat pipes thermal control systems (TCS) for space application. In this paper we will describe how we solved the task of development of the TCS with working fluid of high thermal physical properties. In 2004-2006 we developed the Engineering model of Deployable Radiator based on Loop Heat Pipe by CAST purchase order. It was developed for qualification tests. Ammonia application as LHP working fluid is stipulated by its high thermal physical properties. However Ammonia freezing temperature is of minus 77ºC. Such fact impedes Ammonia application when operation temperatures of LHP Radiator are lower than this value, for example, It takes several tens of hours to orbit a spacecraft and prepare it for work (at that moment the spacecraft is out of power supply) and the working fluid can be frozen in a condenser-radiator when the spacecraft being in the shadow over a long period of time.

Experimental investigation results of developed Axial Heat Pipes with Ω-shape grooves (“Re-Entrant” grooved geometry) are presented in this paper. Influence of working fluid mass and tilt angle on Axial Grooved Heat Pipes characteristics is also described in the paper. Experimental dependence of heat transfer capacity on operating temperature is compared with calculation results. This paper is dedicated to investigation of influence of heat input and heat output sources location on AGHP characteristics under on-ground conditions. Values of heat transfer coefficients in the zones of evaporation and condensation for 3 different AGHP samples are also presented in this paper as well as test results for burst pressure. AGHP qualification test program was developed in accordance with the European Standard (ESA PSS-049).

Two-phase capillary loops are being extensively studied as heat collection and rejection systems for space applications as they appear to satisfy several requirements like low weight, low volume, temperature control under variable heat loads and/or heat sink, operation under on ground and micro gravity conditions, simplicity of mounting and heat transfer through tortuous paths. In 1998–2000 Alenia defined and Lavochkin Association developed the Deployable Radiator on the base of honeycomb panels, axial grooved heat pipes and Loop Heat Pipe. It was designed for on-ground testing.

A universal autonomous controlled heat transferring module on base of two-phase loop with capillary pump have been elaborated. This module consists of one evapourator and one radiator-condenser. Various variants for suggested module control by using of active or passive elements, providing the CPL start-up, restarting and temperature regulation, have been considered. There is determined a structure concept and recommendations on mathematical modeling of Thermal Control System (TCS), made on base of several controlled heat transferring modules with capillary pumps, are given. There are given results of computer experiment with mathematical model of artificial Earth satellite payload TCS. This TCS consists of four controlled, independent in power supply, CPL, which start-up and control are carried out by using of passive devices.

Loop heat pipes (LHP) combine the classical heat pipe operation principle with a loop configuration, i.e. evaporator and condenser are located at separate places as dictated by thermal and configurational reasons and are connected lines for fluid and vapor transport. Experimental investigations of such LHP revealed certain temperature oscillations under certain conditions. This paper presents the results of analyses of such temperature fluctuations and offers possible explanations for initiation and termination of such behavior. Two types of temperature fluctuations have also been confirmed experimentally by testing different kinds of LHP.